It is known in the art that noble metals supported on deacidified alumina are useful for dehydrogenation operations. The deacidified alumina may be prepared by combining the alumina with a Group IIA metal oxide. Examples of these catalysts and their uses may be found in U.S. Pat. No. 2,478,916, U.S. Pat. No. 3,759,823, U.S. Pat. No. 3,696,167 and U.S. Pat. No. 3,763,255. Because all of these patents disclose a hydrocarbon dehydrogenation process, there is no teaching that the catalysts may be physically mixed with an acidic oxide material and that said admixture is useful in hydrocarbon conversion processes requiring an acidic function in the catalyst, e.g., reforming, hydrocracking, isomerization. In fact, the presence of even a small amount of acidity adversely affects the yield of the desired olefinic products produced by a nonacidic dehydrogenation catalyst.
Furthermore, in the above patents, the Group IIA metal oxide is used only to neutralize the acidic support. Thus, the equivalency of magnesium oxide, for example, with the other Group IIA metal oxides is clearly taught.
In the catalyst of the instant invention, the Group IIA metal oxide is utilized to stabilize the catalyst under severe oxidation conditions. The Group IIA metal oxide is selected so as to combine with the transition metal under oxidizing conditions and form a complex oxide of the Group IIA metal and the Group VIII metal. The complex metal oxide is stable to further oxidation and prohibits the growth of large Group VIII metallic or Group VIII oxide or complex oxide crystallites. Thus, in the catalyst of the instant invention, the Group IIA metal oxides, except for magnesium oxide may be used as supports for each of the Group VIII transition metals since complex oxides are formed between these components under oxidizing conditions. Similarly, Group IIA metal oxides, except for magnesium oxide, may be supported on a high surface area refractory oxide, such as silica or alumina in an amount sufficient to (1) neutralize the acidity of the support, if any, and (2) provide an excess to combine with the Group VIII metal. The resulting alumina-Group IIA oxide support stabilizes the Group VIII metals under oxidation conditions. When the Group VIII transition metal is platinum, magnesium oxide may be used as well as the other Group IIA metal oxides in a manner as described above, since platinum is known to form a complex oxide under oxidation conditions with magnesium.
As noted above, when the Group IIA metal is supported on an acidic refractory oxide, such as alumina, a portion of the Group IIA oxide equivalent to the acidity of the alumina is used to neutralize the acidity of the support. In this function, all the Group IIA oxides are equivalent since all will neutralize the acidity present on an acidic refractory oxide support. However, an excess amount of Group IIA oxide over and above that required to neutralize the support is necessary to combine with and stabilize the Group VIII metal under oxidizing conditions. It is this excess that must be capable of combining with the Group VIII metal to produce a complex oxide. In short, for the reasons given above, the Group IIA metal oxides are not equivalent when used to form the catalysts of the instant invention.
The use of Group IIA metal oxides as catalyst supports is taught, in passing, in various patents, for example, see U.S. Pat. No. 2,911,357 which teaches that multimetallic catalysts which include Group VIII metals may be supported on magnesium oxide. However, there is no teaching that these magnesium supported catalysts may be further mixed with an acidic inorganic oxide to provide a catalyst mixture having the acidity required by many hydrocarbon conversion processes including hydrocracking, reforming, etc.
In U.S. Pat. No. 3,789,020, a catalyst comprising a physical mixture containing more than one metal supported on an inorganic refractory oxide support and an additional inorganic oxide support material having no metal supported thereon is taught. The purpose, patentees point out, for preparing the catalyst in this manner, is that they wish to maximize alloy formation on that portion of support containing the metal. Thus, the patentees support the noble metals on a small portion of the total support, for example, one-tenth, and treat this portion of the support under reducing conditions to form the alloy. This portion is then mixed with additional support material to provide a physical mixture wherein the amount of noble metal is at an economical level, for example, less than about 1% by weight. Thus, in effect, the patentees's addition of the excess support material is to provide dilution of the expensive catalyst metals. See also U.S. Pat. No. 3,346,510 wherein the patentees physically admix an acidic refractory oxide with a nonacidic supported Group VIII noble metal catalyst to prepare a bifunctional catalyst. The patentees, however, do not teach, show or suggest the use of a Group IIA metal oxide to stabilize the noble metal from agglomeration under high temperature oxidizing conditions.